I have yet to see anyone with this issue before, I have a Antec 550W PSU and it boots with that, but it when I put the 750W PSU in the CPU fan spins for half a second max and it gives up. I have wired it all up the same with both supply's but no dice. I even unplugged the GPU and nothing. I breadboarded it and nothing. Does the board see the extra wattage as a problem? Both are 80+ Bronze.